1. Field of the Invention
This invention generally relates to a transmission for a bicycle. More specifically, the present invention relates to an internally geared hub for a bicycle.
2. Background Information
Bicycling is becoming an increasingly more popular form of recreation as well as a means of transportation. Moreover, bicycling has become a very popular competitive sport for both amateurs and professionals. Whether the bicycle is used for recreation, transportation or competition, the bicycle industry is constantly improving the various components of the bicycle. Some bicycles are equipped with a transmission for making riding up and down hills easier. One type of bicycle transmission component is an internal hub transmission that is commonly known as an internally geared hub. The internally geared hub has been extensively redesigned over the years.
Bicycles, particularly recreational bicycles referred to as city cruisers, are inexpensive and are easy to ride, and are thus widely used to commute to work or school or for shopping. With this type of recreational bicycle, the internally geared hub is sometimes used in order to ride at high speeds over flat terrain or to ride uphill with minimal exertion.
The internally geared hub generally comprises a hub axle fixed to a bicycle frame and a hub body rotatable about the hub axle. A planetary gear mechanism is housed within the hub body by which rotational drive force can be communicated to the hub body through various transmission paths defined by the planetary gear mechanism. A clutch mechanism including a clutch member is usually provided for selecting the transmission path by selected axial movement of the clutch member, for example by a push rod.
One example of a hub transmission of the above type is disclosed in the European Patent Application No. 0 876 953, where additional structures are provided for facilitating actuation of the clutch member.
In this most conventional hub transmission, the drive member is always in engagement with the clutch member, such that during back pedaling rotation in the backward direction results in reverse rotation not being smooth and somewhat heavy. In order to overcome this drawback, it has been proposed in European Patent Application No. 1 452 437 that an internally geared bicycle hub be configured with a drive member that is rotatably mounted around a hub axle. A hub body is also mounted to rotate about the hub axle, with a planetary gear mechanism being provided for communicating forward rotational force from the drive member to the hub body through various force transmission paths. The planetary gear mechanism includes a planet gear supported by a planet gear carrier for a rotation around the hub axle, a ring gear engaging the planet gear and a sun gear disposed on the hub axle. A clutch member is provided to be movable in axial direction of the axle. Furthermore, a pawl body is arranged between the drive member and the clutch member. A first one-way clutch is arranged to transmit forward rotational drive force from the drive member to the pawl body. Accordingly, the drive member always engages the clutch member through the first one-way clutch to transmit forward rotational motion to the clutch member in any of the selected gear speeds. On the other hand, the first one-way clutch uncouples the drive member from the clutch member when reverse rotational motion is applied to the drive member through back-pedaling. This could, for example, be realized by providing a pawl body between the drive member and the clutch member, where the first one-way clutch is arranged on the pawl body. Consequently it was presumed that the drive member would run smoothly and lightly when back-pedaling because the internal components of the hub transmission are substantially disengaged from the drive member. A smooth backward running of the hub transmission was therefore obtained, which is nearly as light as for example a free hub commonly used with a derailleur.
Although the above described internally geared hub is satisfactory for most applications and even though it allows as described to provide for mounting additionally a multistage sprocket assembly, it has been found that smooth running cannot be always guaranteed, in particular in cases where a large number of sprockets should be mounted to the drive member or in cases where the weight of the bicycle rider is high. In those cases a bending moment can be induced in the internally geared hub, in particular in the drive member or relatively between the mutually coupled hub body and drive member resulting in drag or a heavy running.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved internally geared hub. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.